Field of the Invention
The invention relates to a process for layer production on a surface, in particular a process for layer production on a surface of a semiconductor product.
The manufacture of semiconductor products, in particular of integrated semiconductor products, requires a complex sequence of individual steps. The manufacturing steps in which layers of material are produced on the surface of a semiconductor product assume an important role.
There are a number of processes available for the production of material layers, wherein processes in which the layers to be produced are deposited from the gaseous phase are the ones used most frequently. In particular chemical gaseous phase deposition (CVD=Chemical Vapor Deposition) is one of the most important processes for layer production. The basic principle of CVD is to conduct selected process gasses over a heated surface of a semiconductor product upon which the desired layer is intended to be deposited. A reaction of the process gasses occurs on the hot surface so that on one hand, the desired layer and on the other hand, remainder gasses that must be removed, are produced as reaction products.
The chemical gaseous phase deposition is usually carried out at low pressure in reaction chambers. The semiconductor products to be processed are fed into the reaction chamber and are heated to a predetermined temperature in the reaction chamber. Through the use of one or several gas inlets, the process gasses are supplied to the surface of the semiconductor product and the remainder gasses produced through the reaction of the process gasses are pumped out of the reaction chamber.
If a new semiconductor product is then fed into the reaction chamber for layer production, there is frequently the problem of there still being an aggressive gas in the reaction chamber from the preceding layer production process. That aggressive gas can be a remainder of a process gas used for layer production or it can be a remainder gas produced by the reaction of the process gasses. The aggressive gas can cause undesirable reactions on the surface of the semiconductor product, which damage the semiconductor product.
For example, in the production of tungsten layers, WF.sub.6 is used as one of the process gasses. However, if WF.sub.6 comes into contact with the surface of a Ti/TiN layer, which is used as a contact and barrier layer between silicon and tungsten, then undesirable reactions of WF.sub.6 and titanium can occur: EQU WF.sub.6 +Ti.fwdarw.W+TiF.sub.x.
Those kinds of reactions of WF.sub.6 and titanium break down the Ti/TiN layer or impair the electrical properties (e.g. contact resistances) and can consequently jeopardize the functionality of the semiconductor product. Additionally, if WF.sub.6 comes into contact with a silicon surface, an undesirable reaction can occur, which damages the silicon surface: EQU 2WF.sub.6 +3Si.fwdarw.2W+3SiF.sub.4.